container_of: relicense to Public domain

Too trivial to deserve LGPL, and all my code.

ccan/container_of/LICENSE

@@ -1 +0,0 @@
-../../licenses/LGPL-2.1

ccan/container_of/_info

@@ -46,7 +46,7 @@
  *		return 0;
  *	}
  *
- * License: LGPL (v2.1 or any later version)
+ * License: Public domain
  * Author: Rusty Russell <rusty@rustcorp.com.au>
  */
 int main(int argc, char *argv[])